Conventionally, in a semiconductor integrated circuit such as a semiconductor memory or the like, a potential-detecting circuit for detecting whether the potential of the substrate is higher or lower than a predetermined level, as shown in FIG. 1 (a) and FIG. 1 (b), is formed such that one end of a plurality of diode devices, each connected in series (in FIG. 1(a), diodes D21 through D23, and in FIG. 1(b), transistors Tr 21 through Tr23 connected to diodes), is connected to the substrate, the potential of which is to be measured, and the other end of the series is connected to the power supply potential point (power potential Vcc) via resistor R21 while being entered to an inverter 4A.
In this potential-detecting circuit, the diode device operates as a constant voltage circuit, and the potential Va at the input terminal of the inverter 4A is changed by the same value as substrate voltage Vbb is changed so that this change is detected by inverter 4A to detect the change of the substrate potential Vbb. Incidentally, substrate potential Vbb is normally on a negative level.
In the foregoing conventional circuit, the diode devices working as the constant voltage circuit are connected between the input terminal of the inverter 4A and the substrate to be measured. Since the substrate potential is normally on a negative level, the potential of the electrode of these diode devices often becomes lower than the ground potential. Therefore, when this potential-detecting circuit is incorporated with an integrated circuit including the substrate to be measured and the substrate potential of the potential-detecting circuit is not set to a level below the potential level of the substrate to be measured, current can flow between these electrodes and the substrate, making detection of exact substrate potential impossible.
Further, since diode devices are used as the constant voltage circuit, it is impossible to precisely adjust the potential at both of its terminals. In consequence, the relationship between the substrate potential Vbb and the potential Va at the input terminal of the inverter 4A cannot be precisely adjusted, and this in turn makes it impossible to freely select the potential at which the inverter 4A inverts the output.
In addition, when the power potential Vcc is changed, since the threshold voltage of inverter 4A is changed, the fluctuation of the power potential Vcc also changes the detection level of the substrate potential Vbb at which the inverter 4A inverts the output, even though the potential Va at the input terminal of the inverter 4A does not actually change.